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Heating & Air Conditioning

Wiring a 2 wire Thermostat

14 years ago

I am trying to wire my New Honeywell programmable thermostat. The existing Thermostat uses only 2 wires (for heating and cooling). The switches for Fan operation and Heat/Cool are on the unit itself. I have wired it correctly for heat all winter, but the cooling has me stumped.

When switched to heat, if the 2 wires are connected (jumped) the heat will go on - when disconnected the heater will go off. (this works fine with my thermostat).

When switched to Cool, it is opposite. If the 2 wires are connected the A/C is off, but turns on when the wires are disconnected.

I dont care if I have to rewire this thermostat every season, but I would like to get the thermostat to work with cooling right now. This must be possible in some way, but I have not seen anything on the net about a 2 wire system that heats and cools.

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Comments (2)

funnycide
14 years ago
What kind of thermostat did you have before you bought this programmable tstat? Did you have to rewire each season then? What kind of heat & cool system do you have?
paulbm
14 years ago
is this a trailer or modular home so you have to go to the furnace to switch it to cooling and fan? If so your programable stat will not work on that system. You would have to run new 4 wire and do a lot of rewiring at the furnace.
Later Paulbm
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I disagree with Petey (and with Bus). There is nothing wrong with the thermostat in this application. 410A would have been a better fit but all you're doing is leaving out the second pole on the 410B. You've wired it wrong, though for the life of me I can't think of how you did it. If you'd hooked up the wrong terminals it would be OFF all the time. I suspect you've somehow shorted the wires together separate from the thermostat itself. The color of the wiring isn't particularly obvious. I got it wrong myself (my dumb fault for not reading the instructions). There's not much to this device, the operation is purely mechanical which closes the two switches.
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